This invention relates to a thermal recording head for a thermal recording apparatus and, more particularly, to a thermal recording head having drive circuits and a shift register for supplying picture signals in parallel to thermal resistive elements on an insulated substrate. The incoming picture signals are received in serial form by the shift register, converted to parallel signals and supplied to the drive circuits which drive the thermal resistive elements.
Currently, thermal recording techniques are used in many fields because of easy maintenance and low cost. In such recording techniques, thermal resistive elements are placed in a line and a thermal sensitive paper is passed over the line of elements. The thermal resistive elements are selectively heated to record the image on the thermal sensitive paper.
In prior art thermal recording techniques, matrix circuits are used to decrease the number of lead lines and drive circuits. The matrix circuits are circuits that supply picture signals to separate groups of thermal resistive elements over parallel lead lines. The matrix circuits select one of these groups at a time. However, it is necessary to provide an additional lead line to each group of thermal resistive elements for selecting the particular group to receive the picture signals. The total number of lead lines to each group is more than the number of thermal resistive elements in one group.
To decrease the number of lead lines, a thermal recording head is disclosed in Japanese patent disclosures Nos. 54-48562 and 54-56320 in which shift registers convert incoming serial signals into parallel signals. However, this thermal recording head requires a long time (T=m.multidot.t) to record one line because matrix circuits are used to supply the picture signals from the shift registers to the thermal resistive elements. Here, t is the time necessary to actuate one element and m is the number of groups of thermal resistive elements.
Other types of thermal heads are disclosed in Japanese patent disclosures Nos. 52-105840 and 53-13434. These thermal heads have memory elements associated with each thermal resistive element to store the picture signal so all thermal resistive elements can be actuated at the same time. The picture signals are successively supplied in parallel to each group of memory elements at high speed and then the line of thermal resistive elements is actuated by all groups of memory elements at the same time. However, these thermal heads require a number of lead lines which is greater than the number of thermal resistive elements of one group. Furthermore, these thermal heads require a number of memory elements, which number is the same as the number of thermal resistive elements, and a switch having large current capacity.